This invention pertains to an absorbent polymeric foam composition, more specifically, an absorbent, hydrophilic, polymeric latex foam composition. In other aspects, this invention pertains to a method of preparing the absorbent polymeric latex foam composition and to articles fabricated therefrom.
Absorbent, hydrophilic polymeric foams find utility in products which are used for acquiring and distributing aqueous fluids; for example, diapers, adult incontinence pads and briefs; feminine hygiene products, such as, sanitary napkins and tampons; wiping towels and sponges; wound dressings and surgical sponges; clothing apparel, such as, sweat bands and nursing pads; food packaging, such as, absorbent pads for juice and drippings (for example, chicken juice and meat drippings); cable wrap, and water block tape.
Flexible, hydrophilic, nonionic, polymeric foams which are absorbent, that is, capable of acquiring and distributing fluids, are known wherein the foam is prepared by water-in-oil (w/o) high internal phase emulsion (HIPE) polymerization. As examples of this art, refer to the disclosures of U.S. Pat. Nos. 5,550,167, 5,741,581, and 5,786,395. Disadvantageously, the preparation of a polymerized w/o HIPE foam requires processing large volumes of water, which complicates the foam production process. Moreover, obtaining a dry foam from a w/o HIPE polymerization is difficult. As a further disadvantage, HIPE foams typically require post-synthesis functionalization or rinse treatments in order to render the foam hydrophilic and therefore capable of absorbing aqueous fluids. U.S. Pat. No. 5,741,581 further discloses that the polymeric foam material may be “collapsible,” but expandable upon contact with aqueous fluids. This property is obtained only after extensive post foaming operations. These steps include multiple washing in a hydratable salt solution, with each wash followed by nip rolling. The final nip rolling has to be done under vacuum followed by subsequent drying in an air circulating oven. As yet another disadvantage, HIPE foams may exhibit lower stress at user break, percentage elongation at user break, and toughness, especially when wet, than is desirable for certain absorbent uses.
Latex foams used in absorbent applications are likewise known in the art. For example, U.S. Pat. Nos. 3,887,408, 3,901,240, 4,000,028, and 4,069,366 disclose absorbent pads that comprise a laminate having a crushed polymeric latex foam bonded directly to an absorbent layer or bonded to a non-woven layer which is bonded to an absorbent layer. The pad is prepared by forming a foam, drying it without cross-linking, juxtaposing the foam and laminate layer, crushing the foam under pressure to a specified thickness, and then curing the crushed foam. A foam that is cured after crushing would be expected to have a relatively low void volume and therefore a low free absorbent capacity. Moreover, such a foam would not be expected to expand on contact with aqueous fluids or to vertically wick to a high height.
U.S. Pat. No. 4,990,541 teaches combining latex foam with a starch or cellulose based polymer to make an absorbent article. The latex foam is combined with another polymer to obtain the requirement of high absorption of liquids. U.S. Pat. No. 5,763,067 discloses latex foams having saline uptake values of 1.2 and 7.3 grams of saline solution per gram of latex foam, which is too low for use as an absorbent layer.
Wicking, or the ability to draw fluids away from the point of contact, would be advantageous, because it allows for utilization of regions of the absorbent material far from the point of fluid contact. Vertical wicking, that is, drawing fluids in a vertical direction against gravity, would be highly desirable since it allows for more complete utilization of the absorbent product. By moving the fluid away from the point of contact, wicking may also provide a wearer of the absorbent article with a drier feel to the skin. Traditional latex foams do not normally have the ability to wick fluid from the point of contact. While not wishing to be bound by theory, it is believed that poor wicking may be attributable to the relatively large (greater than 50 μm) cell size found in latex foams.
In view of the above, it would be advantageous to discover a hydrophilic polymeric foam that is capable of acquiring and distributing aqueous fluids, but that is also less complicated to prepare than HIPE foams. It would also be advantageous if the absorbent polymeric foam was inherently hydrophilic, such that post-synthesis functionalization and rinse treatments were not required to achieve hydrophilicity. It would be more advantageous, if the hydrophilic polymeric foam had a high free absorbent capacity. It would be even more advantageous if the hydrophilic polymeric foam was a durable material, as exemplified by good stress at user break, percentage elongation at user break, and toughness, both prior to and after absorbing fluid. Finally, it would be most advantageous if the hydrophilic polymeric foam was capable of vertically wicking aqueous fluids to a high height and rapidly. A polymeric foam composition having all of the aforementioned properties would be highly desirable for use in absorbent applications.